| A new appreciation for the dynamic properties of intermediate filaments (IF) is emerging. The list of diverse functions IF serve continues to lengthen, and it is likely that the dynamic ability of these filaments is critical to their functional role. Vimentin intermediate filaments (VIF) in particular are important in functions related to cell migration, which requires dramatic reorganization of the cytoskeleton. However, the dynamic properties of VIF are not well characterized beyond the motility of immature forms.;Technical advances in imaging, including super-resolution microscopy, combined with newly developed photoconvertible probes are utilized here to show that VIF are dynamic in two ways. First, we found that like the immature forms, mature fully polymerized VIF are transported in a microtubule-dependent manner. VIF were transported along microtubule tracks, even within dense network regions. To characterize this movement, we developed an assay to objectively quantify the transport of intermediate filaments within cells. Using this assay, we showed that VIF transport was independent of microtubule dynamics. Second, we showed that VIF are remodeled in the cell by a robust process of severing and re-annealing rather than by disassembly and reassembly, without any significant contribution of subunit exchange within VIF polymers. We also observed evidence for severing and re-annealing of filaments that persisted even through cell division, at least in SW13 v+ (vimentin containing clone) cells.;Vimentin disassembly occurs in some cell types during cell division due to the presence of nestin (Chou et al. 2003). Therefore, we investigated the relationship between nestin and vimentin in BHK-21 cells. These cells co-express nestin, desmin, and vimentin. We used super-resolution microscopy and platinum-replica immuno-EM to show that in-vivo, as it has been shown in-vitro, nestin and desmin incorporate into the same polymers as vimentin. Furthermore, we showed that the copolymer filaments, like vimentin alone, undergo transport. We discuss the implications of these findings for future research, since copolymerization may regulate dynamics. All together, our results show that intermediate filaments, previously considered the most stable and rigid components of the cytoskeleton, are surprisingly dynamic. We believe that understanding intermediate filaments dynamics will likely serve as the key to elucidating multiple functional roles of IF. |
